The present invention is related to laminated or composite structures employing multiple layers of materials such as those commonly used in the packaging field. In particular, the invention is related to laminated structures employing an interior lamina which provides a barrier to the escape of moisture, flavor, and aroma, such as, for example, aluminum foil or certain polymeric material.
Many items are commonly made from laminated structures employing one or more plastic layers and an interior barrier layer. Conventional collapsible tubes used for packaging such products as toothpaste, shaving cream, shampoo, and the like, are made from such laminated structures. Such tubes are usually impact extruded from a slug of metal after which the tube is decorated, capped, filled, and sealed. Many attempts have been made to replace such metal tubes with plastic tubes, foil tubes, and tubes made from laminates of plastic and foil. Many of these attempts have failed since plastic materials commonly do not provide an adequate barrier to loss of moisture, flavor, and aroma from the contents of the tube. Furthermore, foil tubes are subject to corrosive attack due to the chemical composition of a large variety of commercially packaged products. The most common solution to these problems has been to form a tube from a plastic and metal foil laminated material which has an internal layer of plastic to resist chemical attack, the metal foil serving as a barrier lamina to prevent loss of moisture, flavor, and aroma from the finished tube.
However, when the edges of the laminated structure are overlapped to form a seam, the inner edge of the interior lamina is exposed to the contents of the tube and may interact therewith. Therefore it is desirable to encapsulate the edge of the laminated structure to prevent interaction of the interior lamina or laminae with the contents of the tube.
There are several methods known in the art to accomplish encapsulation of the edge of a laminated sheet or film. One of the most widely employed methods is to apply excessive heat at the seam or edge, forcing a predetermined plastic lamina material to melt and flow over the metal lamina during seaming. Such processes require many stringent conditions during sealing and bonding without assurance that such an encapsulation actually occurs.
Exemplary of the methods of the prior art for encapsulating the edge of a laminated structure to prevent an interior lamina or laminae from reacting with the contents of a container formed from the structure is that shown in U.S. Pat. No. 3,307,738. In this patent, two edges of the laminated structure are overlapped and heat and pressure are applied to cause a reduction in the thickness of the layers and to cause the heat softened thermoplastic layers to flow out and over the edge of the barrier layer or middle layer to form fillets of molten thermoplastic enclosing the respective edges of the barrier layer. These fillets are not only joined together over the edges of the barrier or middle layer but each fillet is pressed into and fused with the corresponding thermoplastic layer of the other lap. Other patents showing encapsulation of the edge of a laminated structure are U.S. Pat. No. 3,976,224; U.S. Pat. No. 3,575,769; and U.S. Pat. No. 3,172,571.